An aircraft mounted gas turbine engine requires an intake to provide a smooth path for the flow of air into the gas turbine engine. The main requirement of the intake is to supply air to the gas turbine engine, under all operating conditions, with minimum loss of energy. The air must be supplied to the gas turbine engine fan and/or compressor at uniform pressure distributed evenly across the whole of the intake area.
At high-speed cruise conditions the airflow velocity into the gas turbine engine is slower than the speed of the aircraft. In the case of a gas turbine engine with an intake mounted under the aircraft wing and at the downstream end of the aircraft wing the lift provided by the aircraft wing helps to reduce the velocity of the air entering the gas turbine engine because of the higher pressure under the aircraft wing, which slows down the air flow in front of the intake mounted under and at the downstream end of the aircraft wing. An intake mounted under and at the downstream end of the aircraft wing interacts favourably with the aircraft wing at high-speed cruise conditions. The intake mounted under and at the downstream end of the aircraft wing requires a relatively small area inlet with relatively sharp lips to reduce spillage drag.
At low speed conditions the airflow velocity into the gas turbine engine is faster than the speed of the aircraft. In the case of a gas turbine engine with an intake mounted over the aircraft wing and at the downstream end of the aircraft wing the lift provided by the aircraft wing helps to increase the velocity of the air entering the gas turbine engine because of the lower pressure over the aircraft wing, which speeds up the air flow in front of the intake mounted over and at the downstream end of the aircraft wing. An intake mounted over and at the downstream end of the aircraft wing interacts favourably with the aircraft wing at low-speed conditions. The intake mounted over and at the downstream end of the aircraft wing requires a relatively large area inlet with relatively thick lips to guide the air into the gas turbine engine at very low speeds.
On the ground, it may be necessary to shield the gas turbine engine intake from ingestion of debris thrown up from the undercarriage of the aircraft. An intake mounted over the aircraft wing provides shielding of the gas turbine engine intake.
Thus, it is clearly seen that different types of intake are required for different applications and/or different flight conditions. It is clear that a high-speed aircraft ideally requires a different intake to that required for a low-speed aircraft or an aircraft on the ground. A high-speed aircraft requires a sharp-lipped intake mounted under the aircraft wing. A low-speed aircraft requires a large thick-lipped intake mounted over the aircraft wing.
A typical prior art solution to the problem provides an intake configured for cruise and auxiliary intakes for low speed operation and additional blocker doors to prevent foreign objects entering the intake. This prior art compromises the aerodynamic flow conditions into the fan and/or the compressor, which may induce aerodynamic instability and unacceptable stresses into components of the gas turbine engine.